Samsung MultiXpress M537x series Service Manual page 333

4) Black and White spot
Description : Dark or blurry black spots occur periodically in the printing.
Probable Cause
The paper path is contaminated by toner residue, debris etc.
The rollers in the imaging unit may be contaminated with
foreign matter or paper particles.
The transfer roller is contaminated or worn out.
The pressure roller or heat roller in fuser unit defective.
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Solution
Clean the paper path.
Replace the imaging unit.
Replace the transfer roller.
1) Turn the machine off.
2) Remove and replace the fuser unit.
3) Turn the machine on.
WARNING
Do not touch the fuser unit while it is hot.
4. Troubleshooting
4-197